Railroad tracks generally comprise a pair of metal rails arranged in a parallel configuration so as to guide and support metal wheels of train cars. Use of these tracks to support heavy loads travelling at high speeds results in the formation of irregularities such as pits, burrs, cracks and deformations along the track surface. These irregularities can create excessive noise and vibrations as the wheels of the train car contact the irregularities. Similarly, the irregularities can also increase the fatigue on the rails and the train cars themselves creating substantial safety and maintenance problems. Although the irregularities can often be easily smoothed out of the track by grinding or milling the surface of each track section in a machine shop, removing each section for regular maintenance is impractical and expensive.
A common method of removing irregularities from the track in situ comprises pulling at least one rotating grinding stone that includes an abrasive surface along the track to grind the track surface so as to smooth out any irregularities without having to remove the section. One of the primary concerns with grinding out the irregularities without removing the track section is ensuring that the entire track surface is contacted by the abrasive surface so as to avoid missing any irregularities. Because of factors including different load weights and configurations of the trains traveling over the rails or even installation factors such as, for example, differing soil conditions beneath the rails, the track surface can wear unevenly along the railway. This makes it even more important that that the entire rail profile be contacted by an abrasive surface during the grinding operation. In response to this requirement, a variety of different grinding configurations have been developed are currently available to grind the entire rail profile.
In a Type 1 grinding configuration, a rotating grinding element rotates in a vertical plane above the rail. The abrasive surface is positioned on a perimeter edge of the rotating element and is beveled or shaped to match the rail profile such that it contacts the entire face of the rail surface as the rotating element is directed along the rail. The drawback of the Type 1 configuration is that the large surface area of the abrasive surface for each rotating element creates a substantial amount of friction requiring a relatively powerful motor to rotate the rotating element. Furthermore, the rotating element is typically rotated such that the abrasive surface travels past the track surface in the direction opposite the direction the rotating element is being pulled down the track to maximize the friction generated by the abrasive pad so as to efficiently grind the track surface. While maximizing the effectiveness of the abrasive pad, the friction created by the grinding acts as a brake slowing the grinding process, which can lead to increased amounts of downtime for the rail line being grinded.
In a Type 2 grinding configuration, the amount of power required to rotate the rotating element and the braking effect of the abrasive surface are both reduced by positioning the abrasive surface on the plane of the rotating element instead of the edge. The rotating element is positioned against the track surface such that the rail approximately bisects the center of the rotating element. By positioning the rotating element such that the rail is located proximate the center of the rotating element, the abrasive surface creates a desirable grinding pattern in which the abrasive surface is drawn across the rail surface perpendicular to the rail rather than parallel to the rail. In this grinding configuration, the abrasive surface of an individual rotating element only contacts a single facet of the rail profile, which significantly reduces the amount of power required to rotate the rotating element. However, in order to grind the entire track surface, a plurality of rotating elements operating in a variety of planes must be used to each contact different facets of the track surface so as to cooperatively grind the entire track surface. The drawback of the Type 2 configuration is that the position of the rotating elements prevents the Type 2 configuration from being successfully used on rail sections having encumbrances such as, for example, an inset in a road or a platform where an upper rail surface is even with a surrounding surface such as a road or platform.
A Type 3 grinding configuration somewhat resembles the appearance of a Type 2 grinding configuration in that it also utilizes a plurality of rotating elements with each rotating element rotating in a different plane so as to engage an individual facet of the rail profile rather the entire track surface. However, the rotating elements of the Type 3 configuration are beveled proximate to the edge of the rotating elements such that the rotating elements can rotate in planes that do not prevent the rotating element from being used in track sections having encumbrances such a roads or platforms. As shown in U.S. Pat. No. 7,156,723 to Nataraj an et al., which is herein incorporated by reference in its entirety, the Type 3 configuration is currently used with grinding processes where the abrasive surface can be easily beveled or shaped to properly contact the track surface. The inherent tradeoff between the Type 2 and Type 3 configuration is that because the abrasive surface of the Type 3 configuration is at the edge of the rotating element, the abrasive surface is drawn across the track surface parallel to the track rather than the more desirable perpendicular grinding pattern found with the Type 2 configuration.
Regardless of the configuration type, the contact between the abrasive grinding pad used in all grinding processes and the metal track surface creates a substantial amount of heat and sparking. As a result, most grinding systems for rail lines are required to include fire suppression systems for combating any fires resulting from sparking along the track. The potential fire risk posed by grinding processes has led to a recent trend in track maintenance to use a milling process to maintain the track instead of a grinding process.
Unlike a grinding process, a milling process uses rotating blades and/or bits to mill down the track surface to remove irregularities rather than using friction generated by an abrasive pad. Milling processes generate less heat and sparking than grinding processes, thereby minimizing the risk of fire. A drawback of milling processes is that the rotating blade or bit assembly must be carefully monitored as the blade or bit can easily cut too deeply into the track surface reducing the operating life of the track or creating an irregularity rather than removing the irregularities. Similarly, the milling blade or bit can become broken or dulled from repeated use. Replacing a broken blade or bit can cause significant delays if the blade or bit breaks in a remote location and a new blade assembly must transported to the work site.
Although significant development has been made in the area of removing irregularities from a track surface, it would be advantageous to further improve upon these current processes.